The present invention relates to a fuel injection system for an internal combustion engine.
There is known a fuel injection pump of the distribution type (reference is made to a published book "AUTOMOTIVE ENGINEERING, NO. 5 DIESEL ENGINE" published on Mar. 20, 1980 by SANKAI-DO) as a typical example of conventional fuel injection systems for a diesel engine.
This is explained referring to FIG. 5. Supply of fuel is effected via an inlet 1 by a feed pump 3 driven by a drive shaft 2 coupled with an output shaft of an engine.
Fuel discharged out of the pump 3 with its pressure being regulated by a pressure regulator valve 18 is supplied to a pump chamber 5 of a pump housing 31.
The fuel within the pump chamber 5 is used for lubrication of moving portions and delivered to a high pressure plunger pump 6 via an admission port 12.
This pump has a plunger 7 which is fixedly secured to a cam disc 8 operatively coupled with a drive shaft 2 such that it is driven via a joint 2A by the drive shaft 2 in timed with the engine revolution speed.
The cam disc 8 has a plurality of face cams, corresponding in number to the number of cylinders of the engine, and it is lifted when one of the face cams 9 rides over a roller 11 rotatable with a roller ring 10. Thus, it reciprocates through a stroke determined by a cam lift.
Thus, the plunger 7 reciprocates while turning about its axis. This reciprocating movement causes fuel coming into via the admission port 12 to be supplied via a distribution port 13 and a delivery valve 14 to a fuel injection nozzle, not shown.
Fuel injection amount is adjusted by axially displacing a control sleeve 16 covering a cut-off port 15 formed in the plunger 7. For example, when the opening of the cut-off port 15 is uncovered by the control sleeve 16 owing to its rightward axial displacement, as viewed in FIG. 5, of the plunger 7, fuel supplied under pressure from a high pressure chamber 6A to the distribution port 13 is discharged toward the pump chamber 5 where a relatively low pressure builds up via the cut-off port 15, causing termination of supply of fuel to the distribution port 13.
Therefore, if the control sleeve 16 is displaced to the right as viewed in FIG. 5 relative to the plunger 7, the termination of fuel injection takes place at a delayed timing, resulting in an increase in amount of fuel injection, whereas if the control sleeve 16 is displaced to the left as viewed in FIG. 5 relative to the plunger 7, the timing at which the fuel injection terminates is advanced, resulting in a decrease in amount of fuel injection.
The control sleeve 16 is mounted on a link lever assembly 19 cooperating with an accelerator pedal such that it is displaced in response to the amount of depression of the accelerator pedal. Concurrently, a governor mechanism 18 driven by the drive shaft 2 effects a correction on the link lever assembly 19, adjusting the amount of fuel injection in such a manner as to keep engine revolution speed at a predetermined constant value corresponding to a depression degree of the accelerator pedal.
This link lever assembly 19 includes a collector lever 21, a tension lever 22, a start lever 23, and a start spring 24.
The collector lever 21 is mounted on a pump housing 31 about a pivot B, and it is biased by a compression spring 25 into pressing engagemet with a full load adjust screw 26.
The tension lever 2 and start lever 23 are rotatably arranged about a pivot A. The tension lever 22 is subject to a bias force of a tension spring 28 which is varied via a control shaft 27 by a control lever 20 as the control lever 22 rotates. This bias force is transmitted to the start lever 23 via the start spring 24, urging the start lever 23 into pressing engagement with a governor sleeve 18f of the governor mechanism 18.
The above-mentioned control sleeve 16 is supported by the start lever 23 via a ball joint 18g.
Therefore, turning the lever 20 in such a direction as to increase tension of a spring 28 causes the tension lever 22 to rotate in a counterclockwise direction, as viewed in FIG. 5, causing the start spring 24 to bias the start lever 23 to rotate counterclockwise, as viewed in FIG. 5, about the pivot A, displacing the control sleeve 16 to the right as viewed in FIG. 5, resulting in an increase in the amount of fuel injection.
The governor mechanism 18 is contained within a main body of the fuel pump at its upper portion, and includes a gear 18a integrally connected to a weight holder 18b to which weights 18c are connected for rotation about connection points 18d. If the weight holder 18b rotates about the governor shaft 18e in response to rotation of the drive shaft 2, the weights 18c rotate also and spread about their connection points 18d due to centrifugal force. For example, if, with the same accelerator depression degree, the engine revolution speed increases, the governor sleeve 18f is pressed to the right and advances toward the start lever 23 since it is coupled with the governor shaft 18e and engaged with the weights 18c. This advancing movement of the governor sleeve 18f causes the start lever 23 to rotate clockwise about the pivot A against the bias of the start spring 24, causing the control sleeve 16 to move to the left as viewed in FIG. 5, resulting in a decrease in the fuel injection amount. This causes a drop in engine revolution speed toward an engine revolution speed value corresponding to a given accelerator depression degree.
The fuel injection timing is controlled by rotating the roller ring 10.
Concretely, since the fuel is injected when each of the face cams 9 of the cam disc 8 rides over the roller 11, if the roller ring 10 rotates, for example, in a direction in opposite to a direction which the cam disc 8 is rotated, the timing at which the face cam 9 rides over the roller 11 is advanced accordingly, so that the fuel injection timing is advanced with respect to the engine crank angle.
The roller ring 10 has a timer slide pin 29 engaged in a timer piston 30 so that it is rotated as the timer piston 30 slides.
The timer piston 30 is slidably disposed in a cylinder 30A to define a high pressure chamber 32 adjacent to one end face thereof, and a low pressure chamber 34 adjacent to the opposite end face thereof. Fuel pressure is admitted to the high pressure chamber 32 via a passage 33 from the pump chamber 5, while the low pressure chamber 34 communicates with the suction side of the feed pump 3, so that the pressure within this chamber is as low as a vacuum pressure. However, the bias force of a spring 35 disposed in the lower chamber 34 pushes the timer piston 30 back toward the high pressure chamber 32. In FIG. 5, the timer piston 30 is illustrated in a position where its axis turned through 90 degrees from its original position although the axis of the timer piston 30 extends in a tangential direction to the rotation of the roller 10. Similarly, for ease of illustration, the axis of the feed pump 3 illustrated in FIG. 5 has been turned through 90 degrees from its actual position.
The fuel pressure in the pump chamber 5 increase in proportion to revolution speed of the feed pump 3, so that the timer piston 30 is biased to move to the left, as viewed in FIG. 5, in response to an increae in engine revolution speed. This causes the roller ring 10 to rotate in a direction opposite to a direction which the cam disc 8 rotates in, resulting in advancement of the fuel injection timing relative to the engine crank angle.
However, the conventional fuel injection system mentioned previously employs a mechanical construction to control a fuel injection amount and an injection timing, so that the mechanical construction inevitably becomes complicated, making assembly of component parts and subsequent adjustment thereof difficult. Since the precision degree of machining a cam disc or the like has a limit, there occur variations of fuel injection amount among different cylinders, so that it is difficult to provide stable engine operation at idling. The fuel injection amount is determined by its duration. The duration is decreased when it is desired to decrease fuel injection amount. This, however, does not necessarily provide fuel supply characteristic which is fit for running condition. For example, this results in providing a poor exhaust gas composition during operation with low load. Besides, the conventional fuel injection system is heavy, and requires increased cost, thus hampering wide spread of diesel engine mounted passenger cars.
The present invention aims at providing a superior fuel injection system which has solved the above mentioned problems.